1. Field of the Invention
The present invention relates to a back light apparatus to be used as a light source of a liquid crystal display panel, and a liquid crystal display apparatus equipped with the back light apparatus.
2. Description of Related Art
A liquid crystal display apparatus performs an image display by controlling an orientation of a liquid crystal put between two electrodes in a liquid crystal display panel to pass or intercept the lights from back lights.
Such a liquid crystal display apparatus has a characteristic in which the visibility of a display image changes according to surrounding brightness. For example, at a bright place, such as an exterior of a house, it is difficult to view the liquid crystal display apparatus if the display luminance thereof is not heightened. On the contrary, at a dark place, such as an interior of a room, it is difficult to view the liquid crystal display apparatus if the display luminance thereof is not lowered.
Accordingly, various techniques for adjusting the display luminance according to a surrounding external light quantity have been conventionally proposed.
For example, Japanese Patent Application Laid-Open Publication No. 2007-140260 proposes a display apparatus that is provided with a photosensor for detecting an external light entering from a display screen to each thin film transistor (TFT) and performs the corrections of color tone values of an image to be displayed on the display screen on the basis of the external light detected by each of the photosensors to perform a display of a suitable display color according to the external light.
Moreover, Japanese Patent Application Laid-Open Publication No. 2007-279179 proposes a luminance adjusting apparatus that is provided with sensors for detecting an external light state on both of the display side and back surface side of a display section and judges the state of receiving the direct rays of the sun according to the difference of the output levels of the two sensors to adjust the luminance of the back lights thereof.
In addition, International Publication WO 2003/050602 discloses a liquid crystal display apparatus that is provided with optical sensors at the four corners of a display panel to control the emission intensities of lights.
However, because the technique disclosed in Japanese Patent Application Laid-Open Publication No. 2007-140260 arranges a sensor to each pixel, the number of parts becomes large. Then, the technique has the problems of causing a rise in cost and making the control of the display apparatus more complicated.
Moreover, since the techniques disclosed in Japanese Patent Application Laid-Open Publication No. 2007-279179 and International Publication WO 2003/050602 arrange the sensors on the edges of the display panels, the sensors detect the external lights at the places different from those of the display panels where the external lights that a user actually views directly enter. As a result, as a screen becomes larger, there arises a problem of generating an error between the light quantity of the actual external lights entering the display panels and that of the external lights to be detected. Moreover, since the techniques disclosed in Japanese Patent Application Laid-Open Publications Nos. 2007-140260 and 2007-279179, and International Publication WO 2003/050602 must attach the sensors for detecting external light quantities onto the display panel sides, the adjustment of the luminance of back lights must be performed in the back light apparatus and the display panels structurally, and the techniques have the problem of a large structural restriction.